The zebrafish is an ideal model system in which to study the effects of genetic mutations on eye development and function. Its retina contains four types of cones as well as abundant rods, and the animals are highly responsive visually, enabling the analysis of visual function by behavioral testing. Electrophysiological recordings from the eyes can also readily be made as well. This project is concerned with the isolation and analysis of visual system mutants induced in zebrafish by chemical mutagenesis techniques. Both recessive and dominant mutations have been induced that affect not only retinal function and development, but also lens development. In addition, a mutant has been isolated that is a model for glaucoma. These mutants, then, provide information not only about basic development and function of various eye structures, but they also provide models of various inherited diseases. Over the next four years, additional mutants that affect the eye will be sought. In addition, further analysis of already identified mutants will continue or be undertaken. The discovery of new mutants is accomplished by observational studies or by behavioral testing. Analyses of mutants include light and electron microscopic studies, immunohistochemistry, in situ hybridization and electrophysiology. In addition, gene expression studies using microarray analysis are carried out in certain cases as well as gene knock-down studies using morpholinos. The project will also seek to develop or adapt additional techniques to zebrafish for the analysis of visual system mutants. So, for example, methodology was developed over the past grant period to measure intraocular pressure in the eyes of zebrafish as well as for the staining of individual cell types (rods) using green fluorescent protein (GFP) and transgenic techniques. In the coming grant period, methodology for recording single cell electrical activity will be further developed, as well as techniques for identifying by, electron microscopy, processes from specific retinal cell types including horizontal cells.